Systems and methods for dispersion of dry powders

ABSTRACT

Systems and methods for preparing and dispersing dry powders are disclosed herein. The system includes a powder feeder, a rotating holder or disc configured to receive an input powder from the powder feeder, and one or more ultrasonic transducers. The ultrasonic transducer is configured to create standing waves, which suspend the input powder within a space above the rotating holder disc for collection and subsequent processing and/or use. Also disclosed herein is an adapter configured to fit existing off-the-shelf powder dispensers that includes an ultrasonic transducer configured to suspend an input powder in midair for collection.

This application is a continuation of U.S. patent application Ser. No.16/556,257, filed Aug. 30, 2019, which claims benefit of and priority toU.S. Provisional App. No. 62/724,699, filed Aug. 30, 2018, and U.S.Provisional Appl. No. 62/893,210, filed Aug. 29, 2019, and is entitledto the benefit of those filing dates.

The complete disclosures, including the specifications, drawings andappendices, of all patents, patent applications, and publications citedherein, including U.S. Provisional App. No. 62/724,699, U.S. ProvisionalApp. No. 62/893,210, U.S. application Ser. No. 11/381,952 (US Pub.2006/0249144), U.S. patent application Ser. No. 16/556,257, and U.S.Pat. No. 8,875,702, are hereby incorporated in their entireties byspecific reference for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to improved systems and methodsof aerosol dispersion of dry powders. More particularly, disclosedherein are systems and methods for preparation and dispersion of drypowder at high concentrations with particles in the micron or nanometersize range using ultrasonic waves.

BACKGROUND OF THE INVENTION

Dispersion of dry powders as aerosols is a technique employed inmanufacturing, medical and environmental technologies, agriculture, andmany other fields. Current aerosol dispersion methods and devices canreliably produce aerosol particles as small as 100 nanometers at varyingconcentrations. Many fields require aerosols at concentrations of over5,000 particles per cubic centimeter. However, currently technologiesstruggle with producing high-concentration aerosol powder over sustainedperiods, particularly when applications require particles with diametersin the nanometer and micron range.

A significant issue with dispersing powders containing particles thatare micrometer or nanometer-sized is their cohesive nature.Nanoparticles and microparticles have a very large surface area tovolume ratio, resulting in high surface energy that creates a tendencyof nanoparticles and microparticles to agglomerate. Thus, the smallerthe particles, the greater the propensity for the particles to bindtogether and the greater the dispersion force required to separate theparticles from one another. Overcoming the forces that tend to keepagglomerated nanoparticles together represents a significant hurdle fordispersion of dry powders.

Current technology designed to separate agglomerated particles typicallyrelies on a venturi tube to create a turbulent flow and shear forcesthrough the convergence of differential air velocities. In suchtechnologies, the air velocity through the venturi tube greatly exceedsthe velocity of the air approaching the tube. Therefore, as particlesare pulled into the venturi, shear forces are created when the two airflows meet, which can dissociate agglomerated particles from oneanother.

Certain technologies employ a turn table or rotating disc, a capillarytube, or a venturi throat to further accentuate the difference in airvelocities. However, the introduction of additional elements or movingparts can create confounding problems with agglomeration. In addition tocohesion with one another, nano/micro powders tend to adhere to surfacesof walls and moving parts while being dispersed. This can cause aproblem as dry particles are pulled through various parts of a particledispersion system, particularly when feeding powder into a venturi tube.For instance, dispersion technologies that employ a capillary tubestruggle with agglomeration. In such systems, the particles often clogthe capillary, which causes a steady drop in concentration of dispersedaerosol particles over time. In many technologies that incorporatemultiple parts, there is a burst of particle concentration at thebeginning of the dispersion followed by a slow decay and eventualstoppage of particle generation. This burst followed by a decrease inconcentration of dry particles within the aerosol occurs because,initially, particles are relatively easily removed from the surface bymechanical or fluid dynamic forces. However, as time progresses,particles that are highly cohesive or difficult to remove create apowder bed, which makes sustained particle generation difficult. Thiscauses “caking” or formation of a semi-rigid mass of powder over a shorttime. Thus, current mechanisms for dispersing dry powder that requiremultiple moving parts are not reliable in producing high concentrationsof small particles over a sustained period.

To overcome the problem of “caking,” the number of moving parts requiredfor introducing powder into a venturi tube should be reduced, and theoverall all process for powder dispersion requires simplification. Thus,there is a need for a powder dispersion system capable of generatingaerosol nanoparticles of cohesive powders at high concentrations forlong periods of time.

SUMMARY OF THE INVENTION

In various exemplary embodiments, systems and methods for the ultrasonicproduction of fine particles for dispersion as aerosol are presentlydisclosed. The presently disclosed embodiments are configured to producestable, high concentrations of aerosol particles at a wide range ofsizes. Embodiments are configured to produce nano/micro particles fromcohesive powders. In embodiments, the system and methods produce asteady and high concentration of aerosol particles for more than onehour. In on embodiment, the system is configured to produce particlesthat comprise a diameter of less than 10 micrometers. Other objects andadvantages of this invention will become readily apparent from theensuing description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic cross-sectional, side view of a system forpreparing aerosol dry powders for dispersion, under one embodiment. Thesystem is shown equipped with an ultrasonic generator and ultrasonictransducer.

FIGS. 2A-B show a top view and front cross-sectional view of anotherembodiment of an ultrasonic aerosol generator.

FIGS. 3A-B show a top view and front cross-sectional view of anotheralternative embodiment of an ultrasonic aerosol generator.

FIG. 4 is a graphical representation showing the stable production offine aerosol particles at a high concentration over time from differentcohesive powders or gasses using the presently disclosed system.

FIGS. 5A-D show scanning electron microscopy (SEM) images of variousparticles and sizes in a native powder form.

FIGS. 6A-D show SEM images of various particles and sizes collected fromthe gas phase after aerosolization via the systems and methods describedherein.

FIGS. 7A-B provide the size distribution of (A) 5 μm Polyimide, and (B)500 nm, 200 nm, and 30 nm TiO₂ aerosol particles obtained using anOptical Particle Sizer (OPS) after de-agglomeration via a low-intensityventuri pump.

FIGS. 8A-B provide the size distribution of particles de-agglomeratedusing a high-intensity venturi pump using (A) an OPS; and (B) anElectrical Mobility Analysis (DMA).

FIGS. 9A-D show SEM images of particles collected downstream of the DMAfor 100 nm TiO₂ aerosol particles after de-agglomeration with ahigh-intensity venturi pump.

FIGS. 10A-D show SEM images of particles collected downstream of the DMAfor 30 nm TiO₂ aerosol particles after de-agglomeration with ahigh-intensity venturi pump.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Detailed descriptions of one or more preferred embodiments are providedherein. It is to be understood, however, that the present invention maybe embodied in various forms. Therefore, specific details disclosedherein are not to be interpreted as limiting, but rather as a basis forthe claims and as a representative basis for teaching one skilled in theart to employ the present invention in any appropriate manner.

The singular forms “a,” “an,” and “the” include plural reference unlessthe context clearly dictates otherwise. The use of the word “a” or “an”when used in conjunction with the term “comprising” in the claims and/orthe specification may mean “one,” but it is also consistent with themeaning of “one or more,” “at least one,” and “one or more than one.”

Wherever any of the phrases “for example,” “such as,” “including” andthe like are used herein, the phrase “and without limitation” isunderstood to follow unless explicitly stated otherwise. Similarly, “anexample,” “exemplary” and the like are understood to be nonlimiting.

The term “substantially” allows for deviations from the descriptor thatdo not negatively impact the intended purpose. Descriptive terms areunderstood to be modified by the term “substantially” even if the word“substantially” is not explicitly recited. Therefore, for example, thephrase “wherein the lever extends vertically” means “wherein the leverextends substantially vertically” so long as a precise verticalarrangement is not necessary for the lever to perform its function

The terms “comprising” and “including” and “having” and “involving” (andsimilarly “comprises,” “includes,” “has,” and “involves”) and the likeare used interchangeably and have the same meaning. Specifically, eachof the terms is defined consistent with the common United States patentlaw definition of “comprising” and is therefore interpreted to be anopen term meaning “at least the following,” and is also interpreted notto exclude additional features, limitations, aspects, etc. Thus, forexample, “a process involving steps a, b, and c” means that the processincludes at least steps a, b and c. Wherever the terms “a” or “an” areused, “one or more” is understood, unless such interpretation isnonsensical in context.

As used herein the term “about” is used herein to mean approximately,roughly, around, or “in the region of” When the term “about” is used inconjunction with a numerical range, it modifies that range by extendingthe boundaries above and below the numerical values set forth. Ingeneral, the term “about” is used herein to modify a numerical valueabove and below the stated value by a variance of 20 percent up or down(higher or lower).

In various exemplary embodiments, the present invention comprises asystem for dry powder dispersion. The system can be configured toproduce dry powder as aerosol in the micron to nanometer size rangewithout the use of moving parts. Embodiments employ ultrasonic energy todisperse dry-powder particles for further de-agglomeration. The systemcomprises at least one ultrasonic transducer configured to produce fineparticles of cohesive powders for continuous dispersion at stable, highconcentrations over extended time periods.

Aerosolization of dry powders can be viewed as a two-step process: Thefirst step is the separation of the interfacial contact between powderparticles and the surface on which they are resting (wall of processequipment or other particles). This requires that sufficient mechanicalenergy greater than the energy of adhesion for a given powder besupplied. The adhesion energy of powder particles follows a distributionthat is affected by the material properties and the particle sizedistribution. For any quantum of mechanical energy applied to disperse apowder, particles with adhesion energy less than the applied energy willbe dispersed while those with adhesion energy greater than the appliedenergy will not be dispersed. As time progresses, more and more of theeasily dispersible particles are removed and mixed with the gas flow,leaving behind powder mass that is composed of highly adherentparticles, thus making the sustained generation of particles at constantnumber concentration challenging. The second step in the aerosolizationof dry powders is breaking up of the agglomerates of particles to formaerosols in the sub-micron size range from nanostructured, agglomeratedpowders. Again, the adhesion between primary particles of the powderscales with inverse size leading to high adhesion energy of thenano-agglomerates. The most convenient way to apply mechanical energy tobreak up the agglomerates is through turbulent kinetic energy of a gasand particle-wall collisions. Depending on the magnitude of the impactforces exerted on the particles, various degrees of de-agglomeration islikely to take place. Detaching powder particles down to individualparticles is extremely difficult, as it requires a high amount ofmechanical energy to overcome the inter-particle adhesion energy.

FIG. 1 shows a schematic view of a system 100 for ultrasonic productionand dispersion of cohesive powders under one embodiment of the presentinvention. This system comprises a rotating disc 110 that receives apowder to be dispersed 105. A powder feeder 120 may be used to introducethe powder to be dispersed 105 into the system. The system furthercomprises an ultrasonic generator 140 coupled to an ultrasonictransducer 150. The system 100 may further include a sampling probe 130and a de-agglomeration setup 160.

In several embodiments, the rotating disc 110 comprises a groove 112configured to receive and hold the powder to be dispersed 105. Inembodiments, the groove 112 forms a continuous circle within a top faceof the rotating disc 110 and extends partially through the rotating disc110. The rotating disc 110 can be comprised of any material suitable forreceiving powder. In embodiments, the rotating disc is comprised ofmetal. The rotating disc can be comprised of an aluminum alloy. In oneembodiment, the disc 110 comprises a 6000 series aluminum alloy. Thealuminum alloy may comprise Aluminum 6061. The rotating disc 110 may beany of various sizes depending on the aerosol dispersion requirements.In portable embodiments, the disc 110 is about 10 mm thick and comprisesa radius of about 140 mm. In one embodiment, the groove is about 10 mmwide and comprises a depth of about 2 mm.

The powder feeder system 120 is configured to introduce powder 105directly into the groove of the rotating disc 110. The powder feedersystem 120 may comprise a funnel 121 for receiving and holding inputpowder. The powder feeder system may further comprise a distributionchannel or tube 123. The funnel 121 and the distribution channel or tube123 may be integral to one another or reversibly linked together. Thefeeder system 120 may further comprise one or more vibrating motorsconfigured to agitate the funnel 123 of the feeder system 120. The oneor more vibrating motors may comprise a rotational speed of about10,000-15,000 rpm. Certain embodiments comprise up to four vibratingmotors.

The funnel may comprise a mesh strainer configured to prevent particleclusters over a given size or diameter from passing into thedistribution channel 123. In embodiments, the strainer allows onlyparticles that are about 1 mm in diameter or less to enter thedistribution channel or tube 123. The mesh strainer may be furtherconfigured to agitate large clusters of powder such that the clustersare broken down to a sufficiently small size to pass therethrough. Anopening of the distribution channel or tube 123 of powder feeder system120 may be disposed over the groove in the rotating disc 110 fordistribution of input powder therein. In operation, the disc 110 slowlyrotates about an axis such that the groove continuously receives thepowder to be dispersed 105 from a powder feeder system 120. The disc 110can be configured to rotate at a speed from about 2 rpms to 10 rpm.

The at least one ultrasonic transducer 150 can be placed anywhere alongor above the rotating disc. In several embodiments, the ultrasonictransducer 150 is suspended above the groove 112 of the rotating disc110 in a location that is distinct from the feeder system distributionchannel 123. As seen in FIG. 1 , the ultrasonic transducer may belocated approximately opposite the feeder system distribution channel.

The ultrasonic transducer 150 is configured to create a resonantultrasonic frequency and a resultant standing wave pattern from pressurewaves in the air column between the transducer 150 and the rotating disc110. In operation, these ultrasonic waves agitate the input powder 105within the groove 112 of the rotating disc 110 to create standing wavesmanifested by levitation of the input powder 105. When the transducer150 is suspended above the rotating disc 110, the distance between theultrasonic transducer 150 and the rotating disc 110 can be adjusted toachieve the desired levitation of the input powder 105. In embodiments,optimal levitation is achieved when the ultrasonic transducer 150 isbetween about 2 to 10 mm above the rotating disc 110. Thus, as therotating disc 110 rotates about its axis, the input powder 105 withinthe portion of the groove 112 below the ultrasonic transducer 150 formsan isolated, dense dust cloud of aerosol particles 107 suspended withinthe space between the rotating disc 110 and the ultrasonic transducer150.

As can be seen, when so suspended, the aerosol particles 107 have nophysical contact with any of the moving parts of the system before beingsampled and removed for further de-agglomeration (as discussed below).This lack of physical contact with the system reduces the accumulationof powder on the surfaces of the system and prevents “caking” to ensuresustained production of high-concentration aerosol particles over longperiods of time. This application is particularly advantageous for usewith cohesive input powders.

As shown in FIG. 1 , a sampling probe 130 can be configured to extract asample of the suspended aerosol 107 between the transducer 150 and therotating disc 110 for analysis. In various embodiments, the samplingprobe 130 is configured to determine the size of fine-particle powdersproduced from the application of ultrasonic energy as described herein.The sampling probe can be connected to a vacuum generator to produce anegative pressure for procurement of aerosol to be sampled.

After ultrasonic excitation and resultant levitation, the aerosolparticles 107 can be directed to the de-agglomeration setup or system160 for further particle separation. Embodiments comprise a vacuumgenerator configured to create a negative pressure that directs theaerosol particles 107 to the de-agglomeration setup 160. In severalembodiments, the de-agglomeration setup 160 comprises a low intensityvacuum or a high intensity vacuum. In some embodiments, a high intensityvacuum comprises more than one venturi acting in tandem with oneanother. An exemplary low-intensity vacuum comprises a TDSS seriesair-operated vacuum pump (available from Air-Vac EngineeringCompany—Seymour, Conn.), and an exemplary high intensity vacuumcomprises an Ultra-Vac Series air-operated vacuum pump (available fromAir-Vac Engineering Company—Seymour, Conn.). The sampling probe 130 canalso be connected to the vacuum generator used in the de-agglomerationsetup.

In embodiments, the de-agglomeration setup 160 comprises a venturi tubeto create shear forces configured to dissociate agglomerated particlesfrom one another.

Also disclosed is a method to increase the efficiency of a dry powderdisperser using the ultrasonic transducer described herein. The methodincludes equipping a dry powder disperser with an ultrasonic transducerand permitting the transducer to levitate an input powder for collectionby a de-agglomeration setup.

In several embodiments, the present invention may comprise an adapterconfigured to be utilized with off-the-shelf powder dispersers. Theadapter comprises an ultrasonic transducer configured to prepare aninput powder for de-agglomeration. The ultrasonic transducer can beconfigured to suspend the input powder such that the powder has nophysical contact with any surface before being collected forde-agglomeration.

In various embodiments described herein, the ultrasonic transducer 150can be configured to produce any frequency in the ultrasonic range. Inembodiments the ultrasonic transducer produces sound waves withfrequencies of about 20 kHz or more. The ultrasonic transducer may beconfigured to produce sound wave frequencies of about 20 kHz to 200 kHz.In several embodiments, the ultrasonic transducer 150 is powered by anultrasonic generator 140.

The systems and methods described herein permit the production of asteady and high concentration of aerosol particles for up to 10 hours, 7hours, 5 hours, 3 hours, or 1 hour. The system can disperse stableconcentrations of dry particles for up to 2 hours. In certainembodiments, the system disperses dry-particle powders for about 1.5hours. By way of nonlimiting example, the device may be configured foruse in various aerosol based additive manufacturing, powder processing,inhalation and dosimetric studies, to name a few applications.

The cloud of aerosol 107 formed from ultrasonic excitation of the inputpowder 105 may comprise any commercially useful particle size. Theaerosol may comprise particles in the nanomolecular size range.Particles may be produced that are smaller than 100 nm. Particles can beless than 100 microns in size. The aerosol 107 may comprise particles assmall as 10 microns in size. In certain embodiments, the aerosolparticles 107 are less than 10 microns in size. Aerosol particles withdiameters as small as 0.1 microns, 0.5 microns, 1 micron, 2 microns, 3microns, 4 microns, 5 microns, 6 microns, 7 microns, 8 microns, 9microns, or 10 microns may be produced through the presently disclosedsystems and methods. The systems and methods described herein canproduce particles between about 0.1 to 0.5 microns in size. Particlesthat are smaller than 0.1 microns in size also may be produced.

The systems and methods disclosed herein are capable of producinghigh-concentration aerosols. Several embodiments produce aerosols atconcentrations up to about 1,000,000 particles per cubic centimeter. Thesystems and methods disclosed herein may produce maximum concentrationsof aerosols that range from about 5,000 particles per cubic centimeterto up to about 1,000,000 particles per cubic centimeter. In embodiments,the present systems and methods produce aerosol concentrations ofbetween about 5,000 particles per cubic centimeter up to about 50,000particles per cubic centimeter. Aerosols comprising concentrations ofabout 10,000 particles per cubic centimeter can be generated through thepresent systems and methods. The concentration of the aerosol particlescan be directly proportional to the number of ultrasonic transducersoperating within the disclosed system. In embodiments, increasing thenumber of ultrasonic transducers increases the maximum aerosolconcentration production capacity of the systems and methods disclosedherein.

Embodiments of the presently disclosed systems and methods are suitablefor aerosolizing any commercially useful material, including, but notlimited to, carbonaceous materials (e.g. carbon nanotubes), metaloxides, amorphous materials, and other materials known in the art ofpowder particle dispersion. The systems and methods herein also may beused to disperse materials including, but not limited to, ceramicmaterials, pollen or agricultural dust, radioactive material, andpharmaceutical powders. Certain embodiments are particularly useful forthe creation and aerosol dispersion of cohesive powders including, butnot limited to, polyimide powders, titanium dioxide, calcium phosphate,silicon carbide, barium titanate, lead zirconate titanate,hydroxyapatite, ferrous oxide, and other powders with strong cohesivetendencies.

FIGS. 2A-B show a top view and cross-sectional view (from a front angleof 45 degrees to the right) of another embodiment of an ultrasonicaerosol generator in accordance with the present invention. A powderfeeder channel or tube 223 introduces powder to be disbursed 205 to abrush 225 above a rotating circular holder, disk or table 210. Rotationis provided by a motor, such as a DC motor 214. The powder is spreadalong the surface of the holder by action of the brush as the holderrotates. The powder then passes under a number of ultrasonic transducers250 a-c suspended above the holder, which agitate the input powder 205as it passes below each transducer to achieve the desired levitation ofthe input powder, as described above. The apparatus may comprise ahousing 290 encompassing the rotatable holder, and a gas inlet 270configured to introduce gas into the housing. This results in multipleor distributed clouds of aerosol particles, which mix with the gas flowfrom the gas inlet 270, and then are removed from the apparatus throughan aerosol outlet 230. In the figure shown, the aerosol outlet ispositioned between the multiple transducers, and may be positionedequi-distant therefrom. The brush achieves greater spead and more evendispersement of the powder on the surface, which enhances the creationof the suspended particle clouds from the multiple transducers, and thusthe production of a steady and high concentration of aerosol particles,particularly nanoparticles, for a sustained period of time.

FIGS. 3A-B show an enhanced version and similar views of the generatorof FIGS. 2A-B. Two powder feeder channels or tubes 323 a, b introducespowder to be disbursed 305 to a corresponding brush 325 a, b above arotating circular holder, disk or table 310. Rotation is provided by amotor, such as a DC motor 314. The powder is spread along the surface ofthe holder by action of the brush as the holder rotates. The powder thenpasses under a number of ultrasonic transducers 350 a-f suspended abovethe holder, which agitate the input powder 305 as it passes below eachtransducer to achieve the desired levitation of the input powder, asdescribed above. The apparatus may comprise a housing 390 encompassingthe rotatable holder, and a gas inlet 270 configured to introduce gasinto the housing. This results in multiple or distributed clouds ofaerosol particles, which mix with the gas flow from the gas inlet 370,and then are removed from the apparatus through an aerosol outlet 330.In the figure shown, the aerosol outlet is positioned between themultiple transducers, and may be positioned equi-distant therefrom.Similarly, the transducers may be evenly spaced around the holder. Thebrush achieves greater spead and more even dispersement of the powder onthe surface, which enhances the creation of the suspended particleclouds from the multiple transducers, and thus the production of asteady and high concentration of aerosol particles, particularlynanoparticles, for a sustained period of time.

FIG. 4 shows a graphical representation of experimental data obtainedafter dispersion. The concentration of two cohesive powders of varioussizes ranging from 5 microns to 500 nm (denoting the primary particlesize) was randomly sampled from a 450-second window of time during ameasurement period that lasted about 30 minutes. The data were obtainedusing 5 μm polyamide powder and rutile titanium dioxide (TiO₂) powdersof 500 nm, 100 nm, and 30 nm mean size of primary input particles. Thereported concentration represents dispersed particles in the 0.3-10 μmrange. As shown in FIG. 2 , the systems and methods described hereinproduced stable concentrations of TiO₂ for all particle sizes and for 5μm polyimide particles. These data confirm that the systems and methodsdisclosed herein can consistently aerosolize a wide range of particlesand particle sizes, including low density materials to high densitymetal oxides, at highly stable and tunable concentrations over extendedperiods of time.

FIGS. 5A-D and 6A-D show SEM images of polyimide and TiO₂ particles ofvarious sizes in their native powder state and those collected in thegas state after dispersion using the systems and methods describedherein. As can be seen, the particles collected following dispersion(FIG. 6 ) showed significantly less agglomeration than those shown inthe native powder state (FIG. 5 ). FIGS. 7A-B show the size distributionof (A) 5 μm Polyimide, and (B) 500 nm, 200 nm, and 30 nm TiO₂ aerosolparticles obtained using an Optical Particle Sizer (OPS) afterde-agglomeration via a low-intensity venturi pump. FIGS. 8A-B show thesize distribution of particles de-agglomerated using a high-intensityventuri pump using (A) an OPS; and (B) an Electrical Mobility Analysis(DMA). FIGS. 9A-D show SEM images of particles collected downstream ofthe DMA for 100 nm TiO₂ aerosol particles after de-agglomeration with ahigh-intensity venturi pump. FIGS. 10A-D show SEM images of particlescollected downstream of the DMA for 30 nm TiO₂ aerosol particles afterde-agglomeration with a high-intensity venturi pump.

In various exemplary embodiments, the presently disclosed subject mattercomprises systems and methods employing a novel dry powder dispersionmechanism to ensure that powder is continuously fed into ade-agglomeration setup at high, stable concentrations over time. Thesystems and methods disclosed herein can be scaled to producecohesive-powder aerosols at a wide range of concentrations and sizes.

Thus, it should be understood that the embodiments and examplesdescribed herein have been chosen and described in order to bestillustrate the principles of the invention and its practicalapplications to thereby enable one of ordinary skill in the art to bestutilize the invention in various embodiments and with variousmodifications as are suited for particular uses contemplated. Eventhough specific embodiments of this invention have been described, theyare not to be taken as exhaustive. There are several variations thatwill be apparent to those skilled in the art. Those skilled in the artwill recognize, or be able to ascertain, using no more than routineexperimentation, numerous equivalents to the specific substances andprocedures described herein. Such equivalents are considered to bewithin the scope of this invention, and are covered by the followingsample representative claims.

What is claimed is:
 1. A system for preparing dry powders fordispersion, comprising: a rotatable holder configured to receive aninput powder; at least one ultrasonic transducer suspected above andadjacent to the rotatable holder, configured to create a standing wavepattern to levitate and suspend particles of the input powder on therotatable holder as it passes the at least one ultrasonic transducer,thereby forming a cloud of aerosol particles in the space between therotatable holder and the at least one ultrasonic transducer.
 2. Thesystem of claim 1, further comprising a powder feeder tube adapted todeliver the input powder to the rotatable holder.
 3. The system of claim1, further comprising a tube with an inlet end proximate the cloud ofaerosol particles and configured to extract particles from said cloud.4. The system of claim 3, wherein the tube is a probe tube.
 5. Thesystem of claim 3, wherein the tube directs the particles to ade-agglomeration system.
 6. The system of claim 3, wherein the tubedirects the suspended particles to an aerosol outlet.
 7. The system ofclaim 2, further comprising a brush attached to the powder feeder. 8.The system of claim 1, further comprising a motor in mechanicalconnection with the rotatable holder.
 9. The system of claim 1, whereinthe rotatable holder comprises a rotary disk or round rotary table. 10.The system of claim 9, further comprising a continuous circular groovein a surface of the rotary disk or round rotary table.
 11. The system ofclaim 2, further comprising a funnel attached to an end of the powderfeeder tube, one or more agitators, and one or more mesh strainers. 12.The system of claim 1, further comprising a housing encompassing therotatable holder, said housing comprising a gas inlet configured tointroduce a gas into the housing.
 13. A method of preparing dry powdersfor dispersion, comprising the steps: directing input powder to arotating disc or holder; and subjecting the input powder to ultrasonicexcitation, wherein the ultrasonic excitation suspends the input powderin a cloud of aerosol particles above the rotating disc.
 14. The methodof claim 13, further comprising the step of extracting particles fromthe cloud for de-agglomeration.
 15. The method of claim 13, furthercomprising the steps of: introducing gas; and extracting particles fromthe cloud of aerosol particles and gas.